Method and device for blasting



I nlted States Patent [1113,537,399

' [72] Inventor Paul H. Miller 2,961,583 11/1960 Sorenson 317/80'lamaqua, Pennsylvania 3,011,096 11/ 1961 Wallack et a1. 317/80 [21]Appl. No. 733,634 3,141,114 7/1964 Jenkins et al.. 317/80 [22] Filed May31,1968 3,167,014 1/1965 Kopito 102/28 Patented Nov. 3, 1970 3,288,06811/1966 Jefferson et a1 1021702 [73] Asslgnee w g f a industries PrimaryExaminer-Verlin R. Pendegrass m g e aware Attorney- Kenneth E. Mulford,Roger R. Horton and Ernest a corporation of Delaware CL Amy [54] METHODAND DEVICE FOR BLASTING 14 Claims 4 Drawing 8g ABs Tll A C T: A methodand blasting device are disclosed for use in initiating up to about 150blasting caps disposed in a [52] U.S.Cl l02/70.2 parallel circuit Theblasting device includes a capacitor f F42) 3/12 delivering preferablyan energy output of between about 210 Fleld of Search 102/28, to about400 watt seconds f energy over a relatively Short 22, 317/ period oftime, and a voltage sensing switch for releasing energy from thecapacitor when the required level of energy out- [56] Reta-em. Cned putis available. The output energy, although sufficient to in- UNITEDSTATES PATENTS itiate up to about blasting caps disposed in a parallelcir- 2,644,117 6/1953 Schmitt el al. 317/80 cuit, is insufficient tocause malfunction by internal arcing of 2,892,128 6/1959 Wolf 317/80 asfew as one electric blasting cap disposed in the parallel cir- 2,908,84710/1959 Bickel et a1 317/80 cuit.

Patented 0v. 3, 1370 3,537,399

Sheet 1 of 2 INVENTOR Paul H. Miller ATTORNEY Patented Nov. 3, 1970Sheet INVENTOR Paul H. Miller mw v0 ATTORNEY METHOD AND DEVICE FORBLASTING such a circuit permits rapid connection of the blasting capswith minimal possibility of error. Typically, the electric blasting capsare initiated with electric energy received from a readily available ACpower line.

One cause of malfunctioning of electric blasting caps and in particularthose of the delay type is the large amount of heat generated by anelectrical are which occurs within an electric blasting cap when anexcessive electrical current is supplied. Although it is recognized thatexcess current may be usefully channeled in the parallel circuit byinclusion of additional blasting caps, both delay and inconvenienceresult unless a simple device is available which is operable forinitiation of either as few as one or as many as about 150 blastcapsdisposed in a parallel circuit.

Malfunctioning of electric blasting caps may occur when gases within thedetonator are heated rapidly and a high internal pressure is soon builtup. The heat and high pressure conditions within the blasting capcause aspeed up in the delay.

timing. If the internal pressure builds up sufficiently, an outwardrupture of the cap wall or a violent dislodging of the cap seal mayresult which rapidly releases the contained hot gases. The effect ofthis action on the blasting operation is unpredictable and varied. Thesudden release of the gases may create conditions under which theburning of the delay element may be retarded, in which case the delaytiming will be slow. Under some conditions, the burning delay elementmay be extinguished in which case the delay element will then fail toinitiate the explosive charge of the detonator. Release of hot gases andflame from within a detonator can ignite the surrounding explosive whichmay burn at first but could eventually convert to detonation within theconfines of a borehold.

' If the delay element is extinguished and the surrounding explosivecharge is ignited, many minutes may elapse before heat from the burningexplosive either causes detonation or initiates the explosive charge ofthe blasting cap which initiatcs the remainder of the burning explosive.Heat generated by the burning explosive may decompose the explosivecharge of the blasting cap and, in such case, the surrounding explosivemay, unpredictably, either burn completely or detonate at any pointbefore it is completely consumed by burning. If the burning element isextinguished by the sudden release of the entrapped gases, and theexplosive charge is not ignited by the hot gases, the shot may failcompletely. Thus, the occurrence of a violent electrical are within adelay electric blasting cap may result in various types of malfunctionssuch as, for example, erratic delay timing, misfire, or a delayeddetonation commonly known as a hangfire.

The various malfunctions caused by arcing occur more frequently when anyof the'various parallel circuit arrangements such as normal parallel,reverse parallel, and closed loop parallel are used with a continuoussource of electrical energy of high potential such as a power line. Whenelectric blasting caps are connected in parallel, the voltage across thebridgewire terminals frequently is high enough to sustain an electricalarc after the bridgewire melts and when a power line of high currentcapacity is used, the arc may generate enough heat within the blastingcap prior to detonation to cause malfunction. Parallel circuitarrangements of delay detonators are often used in the blasting art andthe convenience and advantages of a power line as a source of electricalenergy are well known. Thus, the majority of arcing difficultiesencountered in blasting operations occur when a commonly used circuitarrangement is combined with a commonly used source of electricalenergy.

One approach to solving difficulties encountered in initiat ing electricblasting caps disposed in a parallel circuit is disclosed by MacFarlandin U.S. Pat. No. 3,056,349. MacFarland teaches a blasting circuit forinitiating, in parallel arrangement, delay electric detonators bygenerally applying firing energy insufficient to cause malfunction ofdetonators by internal arcing. Firing current is received from acontinuous source of electric energy, and a quick trip switch isemployed to restrict the time interval over which the current isapplied.

Various other approaches for limiting malfunctioning by arcing ofelectric blasting caps disposed in a parallel circuit such as limitingthe magnitude of the firing current and reducing the resistance insidethe electric blasting caps have realized limited success. Theseapproaches have attempted to limit the energy available for initiatingelectric blasting caps disposed in a parallel circuit based on the factthat energy is a direct function of the square of the firing current,times the internal resistance of the cap, times the duration of time thecurrent is applied.

There are several reasons why various prior art methods of initiatingfrom one up to about 150 blasting caps disposed in a parallel circuit bya single device have not been completely successful in eliminatingarcing malfunctions. One reason is that some of these methods attempt tocontrol only one of the three contributing factors that determine theamount of heat generated inside the cap. If one, or both, of the othercontributing factors become excessive, the limiting effect of the onebeing controlled may be overridden. Another reason is that othersolutions depend on a human decision or action. Hence, human erroreasily negates their effectiveness.

An approach that has been tried in an attempt to eliminate the arcingproblem when firing delay electric caps in parallel is to use acommercially available condenser-discharge blasting machine as the powersource. Such blasting machines have been disclosed by Wolf in U.S. Pat.No. 2,892,128 and Bickel et al. in U.S. Pat. No. 2,908,847. Thissolution suffers from the disadvantage that these blasting machines canfire only a limited number of caps connected in parallel while avoidingmalfunctioning when as few as only one blasting cap is initiated.

Heretofore, no commercially available blasting machine has beenavailable which is rated to fire more than about 50 blasting capsconnected in a parallel circuit. This situation is unsuitable becauseoperators employing parallel circuits of blasting caps desire to employmore than 60 caps and many would desire to employ more than caps in asingle shot by a device which is also capable of initiating as few asone blasting cap without circuit modification and malfunctioningproblems.

It has now been found that by the practice of the present invention,from one to about electric blasting caps may be initiated in a parallelcircuit arrangement without encountering arcing malfunctions. This maybe accomplished without the necessity of a human decision or action;and, hence, misfires due to human error are eliminated. The presentinvention uses output energy as a function of the capacitance andvoltage of a condenser-discharge blasting device. v

Generally stated, the present invention provides a blasting device forinitiating up to about 150 electric blasting caps disposed in a parallelrelation by combining an energy output means capable of deliveringbetween about 2l0 to about 400 watt-seconds of energy over a relativelyshort period oftime from a capacitor having a preferred capacitance ofabout.2.8 X l0 farads to about 5.0 X 10- farads. A voltage sensingswitch is also desirably included in the blasting device for sensing thevoltage of the charge on the capacitor and, after the desired voltagelevel is reached, for discharging the capacitor and providing thedischarged energy to initiate the electric blasting caps of the parallelcircuit. Thus, by using a voltage sensing switch, the present blastingdevice may be operated without opportunity for human error. In anembodiment of the present invention, other voltage sensing means may beemployed in the circuit although with less reliability due toopportunity for human error.

The invention will be further described in connection with theaccompanying drawings which illustrate schematically a circuit which maybe used in the practice of the present invention.

In the drawings:

FIG. 1 illustrates a circuit which may be employed for converting analternating current to a direct current;

FIG. 2 illustrates a circuit of the present invention for obtaining acondenser discharge with controlled energy output;

FIG. 3 illustrates electric blasting caps which may number from one upto about I50 disposed in parallel relation; and

FIG. 4 illustrates in greater detail a preferred embodiment of theblasting device ofthe present invention.

In the drawing of FIGS. 1-3, terminals and 12 are illustrated forreceiving an alternating current from, for example, a power line, analternating current generator or other source capable of supplying an ACvoltage sufficient to charge the capacitor system described hereinafter.Switch 14 may be included in the circuit to control the flow of currentinto the system. Indicator light 16 may be also included for indicatingthe flow of electricity between lines 18 and 20, which lines connectbridge rectifier 22 for conversion of the alternating current to adirect current passing to terminals 24 and 26.

Resistor 28 may be included for limiting the flow of current in line 30to switch 32 having charging position 34 and discharging position 36.When switch 32 is in charging position 34, direct current is receivedfrom terminals 24 and 26 for charging capacitor 38. Capacitor 38 mayappear as one or as a bank of capacitors as desired.

Desirably included in the circuit is electromagnetically operated unit40 exemplified by either a relay coil or solenoid for use in conjunctionwith switch 32 to serve as a voltage sensing switch. The voltage sensingswitch may also be any suitable electronic circuit capable of openingswitch 32 when sensing a particular voltage applied to the energystorage capacitor. Optionally included in the circuit is voltagemonitoring system 42 which may be either a voltmeter for visuallyreading the potential applied to capacitor 38 or a simple indicator lampwhich may light when the required potential is applied to the capacitor.

In operation, when the required voltage is received from terminals 24and 26 for charging capacitor 38, electromagnetically operated unit 40causes switch 32 to flip from charging position 34 to dischargingposition 36. Energy is thus released within about 0.25 second fromcapacitor 38 to terminals 44 and 46 for initiating from one to about 150electric blasting caps 48 disposed in parallel between bus wires 50 and52 without malfunction of as few as one blasting cap because of arcing.

The voltage across terminals 24 and 26 for charging capacitor 38,although illustrated in the drawing to be received from an AC source,may be received from a DC power line, battery, DC generator or the likeprovided that sufficient DC voltage ofa magnitude of about 400 to about500 volts and preferably about 450 volts is available for'chargingcapacitor 38. The charged capacitor upon discharging provides about 210to about 400 watt-seconds of energy within about 0.25 second to initiatefrom one up to about 150 electric blasting caps disposed in a parallelcircuit arrangement.

FIG. 4 illustrates, in greater detail, a preferred blasting deviceprepared by the practice of the present invention. Terminals 54 and 56may receive an alternating current from, for example, a standard 115volt AC outlet. Connected between lines 55 and 57 is a power-onindicator light 58, exemplified by a NE-S 1H neon indicator lamp, inseries with resistor 60, exemplified by a 47,000 ohm, 0.5 watt, wirewound resistor. Line 55 joins one terminal post 62 of switch 66, andline 63 joins a second terminal post 64 of switch 66. Switch 66,exemplified by a spring return, double-pole, double-throw toggle switchhaving a rating of 6 amperes and 125 volts, is illustrated in normalcircuit position when connected to terminal posts 68 and 70. Line 69from terminal post 68 is electrically joined to resistor 72, exemplifiedby a 500 ohm, 50 watt, wire wound resistor; and line 71 from terminalpost 70 is electrically joined to bridge line 73. Bridge line 73connects into bridge rectifier 74 formed, for example, of four diodes76, exemplified by General Electric IN5062 silicon diodes. Adjacentdiode connection lines 75 and 77, to that of bridge line 73, receive anelectric current from the high potential side of a step-up transformer78, exemplified by a Thordarson-Meissner 24Rl00 transformer. Electriccurrent to the low potential side of transformer 78 is received fromlines 57 and 63 when switch 66 is in position providing a closed circuitacross terminal posts 62 and 64.

Corresponding to bridge line 73 for receiving rectified current frombridge rectifier 74 is bridge line 79 electrically joining resistor 80,exemplified by a 1,000 ohm, I00 watt, wire wound resistor, which joinsline 81 illustrated connected to charging position 82 of power relayswitch 84. Illustrated in phantom is switch 84 when connected tocapacitor discharging position 86. Line 87 receives current fromcapacitor discharging position 86 when discharging capacitor 88 forreleasing energy to terminals 90 and 92 by lines 73 and 87. The suppliedenergy to terminals 90 and 92 may be received by the circuit illustratedin FIG. 3 when initiating from one up to about 150 electric blastingcaps disposed in parallel circuit arrangement.

Power relay 84 usefully includes switching coil 94 electricallypositioned between lines 89 and 91. An example of a usefully employedpower relay is that commercially available from Rowan Controller Co.under the designation B-32l-SP1 having a l 10 volt AC coil.

Power relay 84 forms a capacitor discharging element of the voltagesensing switch generally illustrated as switch 32 in FIG. 2, andauxiliary relay 96 forms the voltage sensing element thereof. Auxiliaryrelay 96 is exemplified by that available from Potter and Brumfield,identified generally as a plate relay and illustrated in combinationwith variable resistor 98 to obtain a 450 volt pull-in capability whencombined with power relay 84.

Connected to power relay 84 is line 83 joining capacitor 88 and line 93from resistor 72. Capacitor 88 is further connected to line 73 by lineto complete a charging circuit connection. Capacitor 88, disposedbetween-lines 83 and 95, may be formed of eight 400 microfarad, 500working volt DC electrolytic capacitors connected in parallel; i.e., atotal capacitance of about 3.2 X 10- farad.

Usefully disposed in parallel to capacitor 88 is voltmeter 100 connectedby line 101 to line 93 and by line 103 to line 73. voltmeter 100,exemplified by a 0 --500 DC voltmeter, is usefully included for visuallyreading the potential applied to capacitor 88.

In operation, the blasting device of FIG. 4 receives alternating currentfrom a conventional outlet by terminals 54 and 56. When switch 66 is inthe illustrated normal position, a drain of any residual charge oncapacitor 88 is effected through resistor 72 and connecting lines 69 and71 which is a closed circuit with lines 73 and 95 on one side ofcapacitor 88 and lines 83 and 93 on the opposite side thereof. A safetyfeature thus results in the capacitor drain circuit in that capacitor 88is maintained without charge during nonuse of the blasting device.

When switch 66 is advanced to terminals 62 and 64, current is permittedto flow through lines 63 and 57 to the low potential side of transformer78. On the high potential side of transformer 78, current is receivedthrough lines 75 and 77 by bridge rectifier 74 which convertsalternating current to direct current for charging capacitor 88 by lines73 and 81 when power relay 84 is in the capacitor charging position 82.When the required charge is on capacitor 88, auxiliary relay 96,operated by a minimal amount of current, closes switch 102 with terminal104 and makes available alternating current from line 105 and line 91 tocoil 94 of power relay 84. Power relay 84 is thus caused to rapidlyswitch to capacitor discharging position 86 to release energy fromcapacitor 88 through lines 87 and 73 and provide energy at terminals 90and 92 for initiating up to about 150 blasting caps 48 disposed inparallel circuit between lines 50 and 52 of FIG. 3.

Conveniently disposed between lines 87 and 73 is discharge indicator106, exemplified by a NESlH neon lamp, in series with a resistor 108,exemplified by 140,000 ohm, 2 watt, wire wound resistor, positionedalong line 109. Discharge indicator 106 usefully visually indicates whencapacitor discharge is effected.

The invention is further illustrated by the following example:

EXAMPLE Delay electric blasting caps in the number indicated in-thefollowing table were connected according to standard blasting proceduresin a parallel circuit arrangement and initiated by a blasting devicehaving an energy discharge of a magnitude in the amount indicated from acapacitor having a rating also indicated.

b. Voltage sensing means for sensing a voltage between" about 400 andabout 500 volts across said capacitor means; and

c. Means for automatically discharging said capacitor means into thefiring line of said electric blasting caps when said voltage sensingmeans senses a voltage of between about 400 and about 500 volts acrosssaid capacitor means and such that the energy discharged from saidcapacitor means is between about 210 and about 400 watt-seconds.

5. The blasting device of claim 4 wherein the capacitor means has acapacitance of about 3.2 X t'arads.

6. The blasting device of claim 4 wherein the voltage sensing means isan electromagnetically operated unit.

7. The blasting device of claim 6 wherein the electromagneticallyoperated unit is a relay coil. 8. The blasting device of claim 6 whereinthe electromagnetically operated unit is a solenoid.

TABLE Energy No. of Caps Capacitance Voltage (Watt- Connected Test No.(Famds) (Volts) seconds) in Parallel Results 1 2, 840 l0- 500 355 1 Capfired normally. 2. 2, 840xi0- 500 355 All caps fired normally. 3 xltH450 303 1 Cap tired normally. 4. x1 450 393 20 Allcaps tired normally.5. 4, 970x10 400 398 1 Cap iii'ed normally. 6. 4 .l70)(10- 400 398 20All caps fired normally. 7. 3, 000 (l0- 450 304 1 Cap fired normally. 8.3, 000X10- 450 301 20 All cops fired normally. 9 3, OOOXlO- 450 304 150Do.

It is apparent from the foregoing example that the present blastingcircuit releases energy from a capacitor sufficientto initiate up toabout 150 electric blasting caps disposed in a parallel circuitarrangement while being an energy level ins'ufficient to causemalfunction of any one electric blasting c'ap disposed in parallelcircuit by internal arcing.

it is understood that the foregoing detailed description is given merelyby way of illustration and that many variations may be made thereinwithout departing from this invention.

lclaim:

l. A blasting device for firing one to about 150 bridgewiretype electricblasting caps in parallel comprising:

a. Capacitor means capable of discharging between about 210 and about400 watt-seconds oi'ene'rg'y; and

b. Means for automatically discharging said capacitor means into thefiring line of said electric blasting caps when said capacitor means hasbeen charged suificienitly to discharge about 2l0 to about 400watt-seconds of energy. I

2. The blasting device of claim I wherein said means for sintomaticallydischarging said capacitor means is an electromagnetically o eratedunit.

3. The b asting device of claim I wherein said means for antomaticallydischarging said capacitor means discharges said capacitor means withinabout 0.25 seconds.

4. A blasting device for firing one to about 150 bridgewiretype electricblasting caps in parallel comprising:

a. Capacitor means having a capacitance of about 2.8 x

10- farads to about 5.0 X 10- farads;

electric blasting caps in parallel comprising charging a capacitormeans, said capacitor means being capable of discharging between about 210 to about 400 watt-seconds of energy, and automatically dischargingsaid capacitor means into the firing 1 line of said electric blastingcaps when said capacitor means has been charged sufficiently todischarge about 2l0 to about 400 watt-seconds of energy.

ll. The method of claim 10 wherein an elcctromagnetically operated unitis used to automatically discharge said capacitor means when saidcapacitor has been charged to between about 210 to about 400watt-seconds of energy.

12. The method of claim 10 wherein said energy is discharged withinabout 0.25 seconds.

13. A method of firing one to about 150 bridgewire-type electricblasting caps in parallel comprising charging a capacitor means having acapacitance of about 2.8 X 10- t'arads to about 5.0 X 10- iarads,sensing the voltage across said capacitor as said capacitor is beingcharged, and automatically discharging said capacitor into the firingline of said electric blasting caps when the voltage across saidcapacitor has been sensed to be at a value between about 400 and about500 volts such that the energy discharged from the capacitor means isbetween about 210 and 400 watt-seconds.

14. The method of claim 13 wherein the voltage across said capacitor issensed by an electromagnetically operated unit.

